In an inspection process of a semiconductor device, a probe device is widely employed as an inspection device of a semiconductor wafer (hereinafter referred to as a wafer) As shown in FIGS. 2A and 2B, the probe device includes a loader chamber 1 and a prober chamber 2, and inspects electrical characteristics of semiconductor devices (hereinafter referred to as “devices”) formed on the wafer. Incorporated in the loader chamber 1 are a cassette mounter 3 for mounting thereon a cassette C accommodating therein a plurality (e.g., 25 sheets) of wafers W; a wafer transfer mechanism 4 for transferring wafers W from the cassette mounter 3 sheet by sheet; and a pre-alignment mechanism (hereinafter referred to as a “sub-chuck”) 5 for pre-aligning the wafers W transferred via the wafer transfer mechanism 4. The prober chamber 2 includes a mounting table 6 (hereinafter referred to as a “main chuck”) which is moved in X, Y, Z and θ directions via an XY-table, a linear driving mechanism and a θ driving mechanism; an alignment mechanism 7 which performs alignment of a wafer W in cooperation with the main chuck 6; a probe card 8 disposed above the main chuck and provided with a number of probes 8A; and a test head T interposed between the probe card 8 and a tester (not shown). The probe device further includes a display unit 9 for displaying, e.g., an operational menu and an inspection result.
In the prober chamber 2, after the wafer W is aligned with the probes 8A, the main chuck 6, on which the wafer W is mounted, is index fed while concurrently being elevated, so that the probes 8A are brought into contact with electrodes on the devices formed on the wafer W at a predetermined probe pressure (contact load). The electrical characteristics of the devices are inspected while such a contact state is being maintained. At this time, by overdriving the main chuck 6 relative to the probes 8A by a predetermined amount, the probes 8A are considered to be in electrical contact with the wafer W under a substantially constant contact load.
Recently, however, the number of devices that need to be measured simultaneously (the number of simultaneous measurements) is increasing. For example, the number of simultaneous measurements is as many as 32 and the contact load between the probes 8A and the main chuck 6 is greater than 20 kg. Moreover, the probe card 8 is repeatedly expanded and contracted due to an aging thereof of the probe card 8 or a thermal influence from an accelerated test conducted at a high temperature. As a result, the contact load of the probe card 8 that acts on the main chuck 6 varies despite a constant amount of overdriving of the main chuck 6. Therefore, there is a need for a stabilization of the contact load.
For example, FIG. 3 schematically describes such a phenomenon. The main chuck 6 does not rise up to a target position during an overdrive stage, which is marked by a dashed dotted line in FIG. 3, but instead sinks to a position marked by a solid line in the same drawing due to the contact load exerted on the main chuck 6 by the probe card 8. That is, the main chuck 6 is lowered by a slight amount of distance δ, resulting in a failure to obtain a desired contact load. Consequently, an inspection reliability is reduced. Conversely, if an overdriving amount is determined by predicting an amount of sinking of the main chuck 6, the contact load may become excessively large, to shorten a lifetime of the probe card 8.
The applicant proposed a probe method and a probe device employing a pressure sensor in Japanese Patent Publication Laid-open No. 2001-110857. In case of measuring a load by using the pressure sensor, the pressure sensor detects a pressure based on a deformation of itself. Since the pressure sensor is placed near an operating point of the load, e.g., directly underneath the mounting table, i.e., between the mounting table and the linear driving mechanism, the deformation of the pressure sensor itself increases a displacement of the mounting table. Thus, a certain amount of time is required to correct the load including the is deformation of the pressure sensor itself.
Furthermore, the applicant proposed in U.S. patent application Ser. No. 09/776,686 that a measurement mechanism provided with a linear sensor and a linear scale be installed at a peripheral portion of a support member of the main chuck in order to measure a contact load between the main chuck and the probes. Since, however, the measurement mechanism is disposed at the peripheral portion of the support member of the main chuck, additional space around the peripheral portion of the support member needs to be allocated therefor. Further, there may be produced an error resulting from expansions and contractions of the linear scale due to a temperature change.